KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q119493: NetBIOS over TCP/IP Name Resolution and WINS

Article: Q119493
Product(s): Windows for Workgroups and Windows NT Networking Issues
Version(s): 3.50 4.00
Operating System(s): 
Keyword(s): 
Last Modified: 08-AUG-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0 
- Microsoft Windows NT Server versions 3.5, 3.51, 4.0 
- Microsoft Windows 95 
- Microsoft TCP/IP-32 for Windows for Workgroups, versions 3.11, 3.11a, 3.11b 
-------------------------------------------------------------------------------

SUMMARY
=======

NetBIOS over TCP/IP is the network component that performs computer name to IP
address mapping, name resolution (NETBT.SYS in Windows NT and VNBT.VXD in
Windows for Worgroups and Windows 95). There are currently four NetBIOS over
TCP/IP name resolution methods: b-node, p-node, m-node and h-node.

MORE INFORMATION
================

B-Node
------

When using b-node, broadcasts are used for both name registration and name
resolution. On a TCP/IP network, if the IP router is not configured to forward
the name registration and name query broadcasts, systems on different subnets
will not be able to see each other since they will not receive the broadcasts.
B-node name resolution is not the best option on larger networks because its
reliance on broadcasts can load the network with broadcasts.

Microsoft Modified B-Node
-------------------------

The TCP/IP used in Microsoft Windows NT uses a modified version of b-node name
resolution. Microsoft modified b-node name resolution works in the following
manner:

- The workstation first checks the LMHOSTS cache and, if it finds the NetBIOS
  name, returns the IP address.

- Next, the workstation tries broadcasting to resolve the name (this works in
  the same manner as b-node resolution) and, if the destination system is
  active, it returns its IP address.

- Finally, the workstation (if it is a Windows NT system) will check the
  LMHOSTS file in the \<winnt_root>\system32\drivers\etc directory

P-Node (or Point to Point Node)
-------------------------------

When using p-node name resolution, broadcasts are NOT used for name registration
or name resolution. Instead, all systems register themselves with a NetBIOS Name
Server (NBNS) upon start up. The NBNS is responsible for mapping computer names
to IP addresses and making sure that no duplicate names are registered on the
network. All systems must know the IP address of the NBNS, which is equivalent
to a WINS Server. If the systems are not configured with the correct IP address
for the NBNS, p-node name resolution will not work.

The p-node name resolution method uses directed User Datagram Protocol (UDP)
datagrams and TCP sessions for its communication to and from the NBNS.

The main drawback of p-node name resolution is that if the NBNS cannot be
accessed, there will be no way to resolve names and thus no way to access other
systems on the network.

M-Node (or Mixed Node)
----------------------

M-node uses a combination of b-node and p-node for name resolution. This method
first uses b-node and then p-node, which in theory should increase local area
network (LAN) performance. M-Node has the advantage over p-node in that if the
NBNS is unavailable, systems on the local subnet can still be accessed through
b-node resolution.

M-node is typically not the best choice for larger networks because it uses
b-node and thus results in broadcasts. However, when you have a large network
that consists of smaller subnetworks connected via slow Wide Area Network (WAN)
links, M-node is a preferred method since it will reduce the amount of
communication across the slow links.


H-Node (or Hybrid node)
-----------------------

H-node name resolution, which is currently in RFC draft form, also uses both
b-node and p-node, however it only uses b-node as a last resort. When configured
to use h-node, a system will always first try to use p-node and then use b-node
ONLY if p-node fails. In addition, a system can be configured to use the LMHOSTS
file after p-node fails and before trying b-node.

H-node resolution does not require successful p-node registration for a system to
initialize, however the system will use strictly b-node until p-node
registration succeeds. If the NBNS is unavailable and the system resorts to
using b-node resolution, it will continue to attempt to contact the NBNS so that
it can return to using p-node if the NBNS becomes available.

How WINS Works
--------------

By default, when a system is configured to use WINS for its name resolution, it
adheres to h-node for name registration. For name resolution, it will also
adhere to h-node but with a few differences. It will:

- Check to see if it is the local machine name.

- Check its cache of remote names. Any name that is resolved is placed in a
  cache where it will remain for 10 minutes.

- Try the WINS Server.

- Try broadcasting.

- Check the LMHOSTS file, if the system is configured to use the LMHOSTS file.

- Try the HOSTS file and then a DNS, if so configured.

Additional query words: prodnt

======================================================================
Keywords          :  
Technology        : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT351search kbWinNT350search kbWinNT400search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS400search kbWinNTS400 kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search kbAudDeveloper kbWin95search kbTCPIPSearch kbZNotKeyword3 kbTCPIP311 kbTCPIP311a kbTCPIP311b
Version           : 3.50 4.00

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.